Nanotube sensor

ABSTRACT

A sensor having a nanotube grown on and supported by thermal bimorph structures. The nanotube rests on a heat sink during sensing gas or a liquid and is moved from the heat sink when the nanotube is heated to desorb gas or liquid from it. The heatsink may function as a gate along with the bimorph structures as the other terminals of a transistor. Current-voltage and current-gate voltage characteristics may be obtained of the nanotube as a device like a transistor. These characteristics may provide information on a gas or liquid absorbed by the nanotube.

BACKGROUND

The invention pertains to gas sensors. Particularly, it pertains tonanotube sensors.

Certain attempts have been made to use nanotube for gas sensing. U.S.patent application Ser. No. 10/100,440, filed Mar. 18, 2002 andentitled, “Carbon Nanotube Sensor,” is hereby incorporated by reference.

SUMMARY

Nanotubes can be grown in-situ in a directed manner in a certain gasenvironment by bridging a moat between two moveable finger-or arm-likesupport pieces, connections or electrodes for the nanotubes. Amanufacturable MEMS-base nanotube sensor can be made.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 a and 1 b show a sensor structure that supports a nanotube.

FIGS. 2 a and 2 b show a sensor structure that has a nanotube.

FIGS. 3 a and 3 b show electrical configurations of a nanotube sensor.

FIG. 4 is a graph of current-gate voltage curves of several gasesabsorbed by a nanotube of a sensor.

FIG. 5 is a flow diagram of a process of a nanotube sensor.

FIGS. 6 a and 6 b show a nanotube sensor having a cross-bar likestructure.

FIGS. 7 a and 7 b are cross-section views of a nanotube sensor similarto that in FIG. 6 a.

FIGS. 8 a and 8 b are cross-section views of a nanotube sensor similarto that in FIG. 6 b.

DESCRIPTION

FIG. 1 a shows a basic structure that supports a nanotube. Bimorphfinger- or arm-like longitudinal structures 11 and 12 are situated onsubstrate 10. A pedestal-like structure 13 may be situated between theends of structures 11 and 12 on substrate 10. Structure 13 may beutilized as a heat sink or an electrode or both.

Structures 11 and 12 may be composed of a top metal layer 21 and abottom 22 dielectric, or vice versa. These structures may have othercompositions. In FIG. 1 b, structures 11 and 12 may be heated and theirends will move away from structure 13 and substrate 10 due to the heat.

In FIG. 2 a, while fingers or arms 11 and 12 are raised up, one or morenanotubes may be grown bridging the two closer ends of structures 11 and12. This growing may be performed in an atmosphere or local environmentof ethylene, methane, CO or the like. A nanotube or nanotubes are grownupon heating the structures to between approximately 700 and 900 degreesCelsius. Generally, one may result, in having a carbon single-walled(i.e., one layer of molecules) nanotube 15 bridging the ends facing eachother of structure 11 and 12. The nanotube may grow by virtue of flowand/or an electric field from one end to the other of structures 11 and12. When device 14 is removed from the heat of a furnace or other heatsource, structures 11 and 12 cool and their ends 16 and 17 move towardssubstrate 10 as shown in FIG. 2 b. This activity causes nanotube 15 tosit on heat sink/electrode 13. Structure 13 may be composed of a metal19 that has been coated with a thin passivation layer 18. Device 14 canbe cut out as a die and mounted on a header for operation.

When nanotube 15 has cooled down, it may be exposed to a fluid andabsorb some of it. A fluid may be a gas or a liquid. “Gas” is to bereferred to in this description but may be interchanged with “liquid”.When device 14 is heated as a die, nanotube 14 is lifted off of post orpedestal 13 by structures 11 and 12 when the latter bend as a result oftheir bimorph structures being heated. When nanotube 15 is heated,absorbed gases are driven off nanotube 15, making it ready forresorption of new gases. When the heat is removed, arms 11 and 12 comedown; nanotube 15 sits on heat sink 13 which removes heat from nanotube15. Then nanotube 15 is ready for resorption of new gas in the sensor'simmediate environment.

To lift nanotube 15 off of heat sink 13, arms 11 and 12 may be actuatedseveral different ways. Device 14 as a die on a header 20 may be heatedor structure 11 and 12 may have heating elements in them. In eithercase, nanotube 15 is removed from contact with heat sink 13 so thatnanotube 15 can more rapidly heat up and desorb any gas on it, as shownin FIG. 2 a. After this, heat is removed from header 20 or heatingelements 23 in arms 11 and 12 are disconnected. Structures 11 and 12move towards substrate 10 and nanotube 15 rests on heat sink 13 tofurther cool off and be ready for absorption of a new gas.

FIG. 3 a shows an electrical configuration which may be used to aid inidentifying a gas absorbed by nanotube 15. Power supply 24 is connectedto structure 11 and 12 which become connections to nanotube 15. Thecurrent indication from meter 26 and the voltage indication from meter25 may be noted, and from such IV characteristics, information about oridentification of a gas or liquid absorbed by nanotube 15 may beobtained.

FIG. 3 b shows a three terminal electrical configuration resembling afield effect transistor having a power supply 27 and a meter 28 formeasuring gate-voltage. Structure 13 is the gate and structures 11 and12 are the source and drain, respectively. The other electrical aspectsof this figure are similar to those shown in FIG. 3 a. The current (I)meter 26 and the gate voltage (V_(g)) meter 28 may be noted, and fromsuch IV_(g) characteristics, information about or identification of agas or a liquid absorbed by nanotube 15 may be obtained. On the otherhand, for a predetermined V_(g) set by power supply 27, the current frommeter 26 and the voltage from meter 25 may be noted, and from such IVcharacteristics, information about or identification of a gas or liquidabsorbed by nanotube 15 may be obtained. The above readings may be takenperiodically over a period of time from the moment that a gas begins tobe absorbed by nanotube 15. Such IV and IV_(g) characteristics mayprovide additional information, such as concentrations of the gas orliquid in the environment of nanotube 15.

FIG. 4 is an example of IV_(g) characteristics for several gasesabsorbed by device 14 in FIG. 3 b. Curve 31 shows the IV_(g)characteristics before gas absorption by nanotube 15. Curve 32 showsthat IV_(g) characteristics after absorption of NH₃ by nanotube 15.Curve 33 shows the IV_(g) characteristics after absorption of NO₂ bynanotube 15. Absorption of each gas would occur after any gas or liquidin nanotube 15 was desorbed or removed. The nanotubes could befunctionalized with different materials (metals, organics,semiconductors) to enhance response and discrimination for differentgases.

FIG. 5 shows a flow diagram 30 outlining the gas/liquid sensing processof device 14 as described above. Block 34 is exposure of nanotube 15 tothe gas and/or liquid. Measuring the IV and/or the IV_(g)characteristics of nanotube 15 is represented by block 35. Next, inblock 36, nanotube 15 is moved away from heat sink 13 by supportstructures 11 and 12 with heat.

Heat is also used to drive off gas/liquid from nanotube 15, asrepresented by block 37. In block 38, structures 11 and 12 are cooledand return nanotube 15 to rest on heat sink 13 to further cool. Path 39shows that the sensing process may repeat for sensing another or thesame gas or liquid.

FIG. 6 a reveals a plan view of a sensor 41 having a structure orcrossbar 40 that may be a heat sink and/or an electrode of a transistorfor purposes of attaining IV_(g) characteristics of nanotube 15,particularly for gas/liquid sensing. Structures 47 and 48 may be theother connections to the transistor, i.e., nanotube 15. FIGS. 7 a and 7b show a cross-section view of device 41. Nanotube 15 is situatedbetween crossbar 40 and substrate 43. Structures 47 and 48 may haveheating elements to heat them and nanotube 15, or substrate 43 may beheated for a similar effect. Upon heating, structures 47 and 48 lowernanotube 15 off of heatsink 40. Upon cooling, nanotube 15 is brought upto heatsink 40 and nanotube 15 is further cooled by structure 40. Theremay be an inverted pyramid-shaped pit 44 etched in substrate 43, forcooling or other reasons. Some other aspects of device 41 for gas/liquidsensing are like that of device 14.

FIG. 6 b shows a device 42 which has a crossbar, heatsink or gate-likestructure 40 situated between nanotube 15 and substrate 43. Along withstructure 40, structures 45 and 46 which are connected to nanotube 15,and with configurations like those of device 14 in FIGS. 3 a and 3 b,one may get IV and IV_(g) data of nanotube 15 with or without anabsorbed gas or liquid. FIGS. 8 a and 8 b show a cross-section of device42. Finger- or arm-like longitudinal structures 45 and 46 that holdnanotube 15 are like that of structures 47 and 48 of device 41 exceptthat they move away from substrate 43 rather than towards it, whenheated. When structures 47 and 48 cool down, they move towards substrate43 and nanotube 15 may be set on heatsink structure 40 for furthercooling. There may be a pyramid-shaped pit 44 in substrate 43 topossibly improve cooling or facilitate other reasons for device 42. Orthere may not be a pit 44. Many aspects of device 42 are like those ofdevices 14 and 41 for gas/liquid sensing.

Longitudinal structures 45, 46, 47 and 48 may be etched, at least inpart, from substrate 43, or be formed on substrate 43. Structure 40 maybe made in a similar fashion like that of structures 45, 46, 47 and 48.The structures of devices 14, 41 and 42 may be MEMS technology or becompatible with it. The technology of these devices may be silicon basedor of another material.

Although the invention has been described with respect to at least onespecific embodiment, many variations and modifications will becomeapparent to those skilled in the art upon reading the presentspecification. It is therefore the intention that the appended claims beinterpreted as broadly as possible in view of the prior art to includeall such variations and modifications.

1. A nanotube sensor comprising: a first structure; a second structurehaving a first end attached to said first structure, and having a secondend; a third structure having a first end attached to said firststructure, and having a second end; at least one nanotube attached tothe second ends of said second and third structures; and a fourthstructure situated on said first structure and proximate to said atleast one nanotube; and wherein the second ends of said second and thirdstructures may move relative to said first structure upon a change oftemperature.
 2. The sensor of claim 1, wherein said fourth structure mayabsorb heat.
 3. The sensor of claim 2, wherein said at least onenanotube may be close to said fourth structure.
 4. The sensor of claim3, wherein a change of temperature of said second and third structuresmay cause said at least one nanotube to be moved away from or closer tosaid fourth structure.
 5. The sensor of claim 4, wherein acurrent-voltage (IV) characteristic of said at least one nanotube ismeasurable.
 6. The sensor of claim 5, wherein said at least one nanotubeis exposable to a fluid.
 7. The sensor of claim 6, wherein the fluid maybe a gas and/or liquid.
 8. The sensor of claim 7, wherein the IVcharacteristic of said at least one nanotube may indicate to what kindof fluid said at least one nanotube is exposed.
 9. The sensor of claim8, wherein heating said at least one nanotube may remove a significantportion of a fluid gas to which said at least one nanotube was exposed.10. The sensor of claim 9, wherein the heating may result in said secondand third structures to move said at least one nanotube away from saidfourth structure.
 11. The sensor of claim 10, wherein a movement of saidat least one nanotube away from said fourth structure may result inincreased heating of said at least one nanotube.
 12. The sensor of claim11, wherein cooling may result in said second and third structures tomove said at least one nanotube closer to said fourth structure.
 13. Thesensor of claim 12, wherein a movement of said at least one nanotubecloser to said fourth structure may result in increased cooling of saidat least one nanotube.
 14. The sensor of claim 13, wherein said at leastone nanotube may be heated by said second and third structures.
 15. Thesensor of claim 14, wherein said second and/or third structures have abimorph composition.
 16. The sensor of claim 13, wherein said at leantone nanotube is heated by said first structure.
 17. The sensor of claim16, wherein said second and/or third structures have a bimorphcomposition.
 18. The sensor of claim 4, wherein: said sensor is like atransistor; and said second, third and fourth structures are a source, adrain and a gate of the transistor, respectively.
 19. The sensor ofclaim 18, wherein a current-gate voltage (IV_(g)) characteristic of thesensor is measurable.
 20. The sensor of claim 19, wherein said at leastone nanotube is exposable to a fluid.
 21. The sensor of claim 20,wherein the fluid may be a gas or liquid.
 22. The sensor of claim 21,wherein the IV_(g) characteristic may indicate to what kind of fluidsaid at least one nanotube is exposed.
 23. The sensor of claim 22,wherein heating said at least one nanotube may remove a significantportion of a fluid to which said at least one nanotube was exposed. 24.The sensor of claim 23, wherein the heating may result in said secondand third structures moving said at least one nanotube away from saidfourth structure so as to increase the temperature of said at least onenanotube.
 25. The sensor of claim 24, wherein the cooling may result insaid second and third structures moving said at last one nanotube closerto said fourth structure so as to decrease the temperature of said atleast one nanotube.
 26. The sensor of claim 25, wherein at least one ofsaid second and third structures has a thermal bimorph composition. 27.The sensor of claim 26, wherein at least one of said first, second,third and fourth structures is made with a MEMS based process.
 28. Ananotube sensor comprising: a first structure; a second structure havinga first end attached to said first structure, and having a second end; athird structure having a first end attached to said first structure, andhaving a second end; at least one nanotube attached to the second endsof said second and third structures; and a fourth structure situated onsaid first structure and proximate to said at least one nanotube; andwherein said at least one nanotube is situated between said firststructure and said fourth structure.
 29. The sensor of claim 28, whereinsaid fourth structure has first and second ends attached to said firststructure.
 30. The sensor of claim 29, wherein a current-voltage (IV)characteristic of said at least one nanotube is measurable.
 31. Thesensor of claim 30, wherein: said at least one nanotube is exposable toa fluid; and the fluid may be a gas and/or liquid.
 32. The sensor ofclaim 31, wherein the IV characteristic of said at least one nanotubemay indicate to what kind of fluid said at least one nanotube isexposed.
 33. The sensor of claim 29, wherein: said sensor is like atransistor; and said second, third and fourth structures are like asource, a drain and a gate of transistor, respectively.
 34. The sensoror claim 33, wherein a current-gate voltage (IV_(g)) characteristic ofthe sensor is measurable.
 35. The sensor of claim 34, wherein; said atlast one nanotube is exposable to a fluid; and the fluid may be a gasand/or liquid.
 36. The sensor of claim 35, wherein the IV_(g)characteristic may indicate to what kind of fluid said at least onenanotube is exposed.
 37. The sensor of claim 36, wherein: heating saidat least one nanotube may remove a significant portion of a fluid towhich said at least one nanotube was exposed and absorbed; and coolingsaid at least one nanotube may enable reabsorptance of a fluid.
 38. Thesensor of claim 37, wherein said second and third structures uponheating move said at least one nanotube away from said fourth structureand upon cooling move said at least one nanotube towards said fourthstructure.
 39. The sensor of claim 38, wherein said second and thirdstructures have a temperature bimorph structure.
 40. The sensor of claim37, wherein said fourth structure is a longitudinal structure situatedapproximately non-parallel to said at least one nanotube.
 41. The sensorof claim 40, wherein said first structure has a pit proximate to said atleast one nanotube.
 42. A nanotube sensor comprising: a first structure;a second structure having a first end attached to said first structure,and having a second end; a third structure having a first end attachedto said first structure, and having a second end; at least one nanotubeattached to the second ends of said second and third structures; and afourth structure situated on said first structure and proximate to saidat least one nanotube; and wherein: said at least one nanotube issituated between said fourth structure and said first structure; andsaid fourth structure has first and second ends attached to said firststructure.
 43. The sensor of claim 42, wherein: a current-voltage (IV)characteristic of said at least one nanotube is measurable; said atleast one nanotube is exposable to a fluid; the fluid may be a gasand/or liquid; and the IV characteristic of said at least one nanotubemay indicate to what kind of fluid said at least one nanotube isexposed.
 44. The sensor of claim 43, wherein: said sensor is like atransistor; said second, third and fourth structures are like a source,a drain and a gate of the transistor, respectively; a current-gatevoltage (IV_(g)) characteristic of the sensor may be measurable; said atleast one nanotube may be exposable to a fluid; the fluid is a gasand/or liquid; and the IV_(g) characteristic may indicate to what kindof fluid said at least one nanotube is exposed.
 45. The sensor of claim44, wherein said fourth structure is a longitudinal structure situatedapproximately non-parallel to said at least one nanotube.
 46. The sensorof claim 45, wherein said first structure has a pit proximate to said atleast one nanotube.
 47. The sensor of claim 45, wherein said second andthird structures upon heating move said at least one nanotube away fromsaid fourth structure and upon cooling move said at least one nanotubetowards said fourth structure.
 48. The sensor of claim 47, wherein thesensor is made with a MEMS-based process.
 49. A nanotube sensorcomprising: a substrate; a first longitudinal projection on saidsubstrate; a second longitudinal projection on said substrate; and atleast one nanotube grown and connecting first and second longitudinalprojections; and wherein said first and second projections, when heated,move away from said substrate, and when cooled, move towards saidsubstrate.
 50. The sensor of claim 49, wherein: said projections have anambient environment of ethylene, methane, CO or other like fluid; theenvironment is heated to a temperature sufficient to move saidprojections away from said substrate, the temperature is sufficient togrow said at least one nanotube; and after the said at least onenanotube is grown, the environment cools down and said projections,along with said at least one nanotube, move towards said substrate. 51.A nanotube sensor comprising: a substrate; a first longitudinalprojection on said substrate; a second longitudinal projection on saidsubstrate; at least one nanotube grown and connecting first and secondlongitudinal projections; and a heat sink structure which said at leastone nanotube can be situated upon a moving of said first and secondprojections towards said substrate; and wherein: said at least onenanotube can absorb a gas/liquid in a proximate environment; andcurrent-voltage (IV) characteristics of said at least one nanotube mayreveal information about the gas absorbed.
 52. The sensor of claim 51,wherein: upon heating said first and second projections, said at leastone nanotube is moved away from said heat sink structure and heatedthereby desorbing a significant portion of gas/liquid on said at leastone nanotube; and upon cooling said first and second projections, saidat least one nanotube may be moved to said heat sin structure to cooland may absorb some gas/liquid.
 53. The sensor of claim 52, wherein:said sensor is like a transistor in that said first projection, saidsecond projection and said heat sink structure are like source, drainand gate connections of the transistor; and current-gate voltage (IV)characteristics of said at least one nanotube may reveal realinformation about a gas absorbed by said at least one nanotube.
 54. Ananotube sensor comprising: a substrate; a first longitudinal projectionon said substrate; a second longitudinal projection on said substrate;and at least one nanotube grown and connecting first and secondlongitudinal projections; and wherein said first and second projectionsmove in a first direction when heated and move in a second directionwhen cooled.
 55. The sensor of claim 54, further comprising alongitudinal strip having first and second ends attached to saidsubstrate.
 56. The sensor of claim 55, wherein: said at least onenanotube is situated between said longitudinal strip and said substrate;and said first and second projections are like a source and a drain,respectively, and said longitudinal strip is like a gate of atransistor.
 57. The sensor of claim 56, wherein a current-voltagecharacteristic of said at least one nanotube may indicate informationabout a gas absorbed by said at least one nanotube.
 58. The sensor ofclaim 56, wherein a current-gate voltage characteristic of said sensormay indicate information about a gas absorbed by said at least onenanotube.
 59. The sensor of claim 55, wherein: said longitudinal stripis situated between said at least one nanotube and said substrate; andsaid first and second projections are like a source and a drain,respectively, and said longitudinal strip is like a gate of atransistor.
 60. The sensor of claim 59, wherein a current-voltagecharacteristic of said at least one nanotube may indicate informationabout a gas absorbed by said at least one nanotube.
 61. The sensor ofclaim 59, wherein a current-gate voltage characteristic of said sensormay indicate information about a gas absorbed by said at least onenanotube.